1. Field of the Invention
The present invention relates generally to a method and apparatus for monitoring the carry through condition of a mechanical press. A mechanical press tends toward a dynamic carry through condition as the kinetic energy buildup present within the slide exceeds the kinetic energy and load requirements of the application needed to blank or form the part and thus, reduces or eliminates bounce, rebound, or dwell experienced as the slide contacts the stock material is reduced or even eliminated. Specifically, the present invention utilizes characteristics of an actual slide displacement curve to determine the operational state of a press being monitored relative to a dynamic carry through condition.
2. Description of the Related Art
Mechanical presses of the type performing stamping and drawing operations employ a conventional construction which includes a frame structure having a crown and a bed and which supports a slide in a manner enabling reciprocating movement toward and away from the bed. These press machines are widely used for a variety of workpiece operations and employ a large selection of die sets with the press machine varying considerably in size and available tonnage depending upon its intended use.
The flywheel assembly serves as the primary source of stored mechanical energy and rotary driving power in a mechanical press. Standard press configurations have the flywheel located between the main drive motor and clutch, with the flywheel being mounted on either the driveshaft, crankshaft or press frame by the use of a quill. The main drive motor replenishes the flywheel with rotational energy as it becomes depleted due to press stamping operations, during which the clutch engages the flywheel and establishes a driving connection between the flywheel and the crankshaft. When the crankshaft and flywheel are engaged in driving relationship, the flywheel energy is usefully converted into mechanical work to power the press components including the slide. During engagement of the clutch, the flywheel drops in speed as the press driven parts are brought up to running speed.
During press operation, the slide reciprocates up and down creating inertial forces on the press components. Balancer weights are utilized to dynamically balance these inertial forces. Guides are supplied to provide slide and balancer weight motion in the desired direction. As press speed increases, the vibration severity levels of the application within the press generally escalates.
As the press slide contacts the stock material and progresses to sheer material, the stock material fractures through and the release of stored energy sends a vibration shock wave through the press structure. When the slide contacts the stock material, it experiences a xe2x80x9cbouncexe2x80x9d or xe2x80x9cdwellxe2x80x9d as the slide movement is resisted by the stock material. This bounce at the snap through point of the stock material causes a decrease in the slide""s kinetic energy, which energy must be replenished by the flywheel. Tending towards substantially eliminating slide bounce or dwell, as the slide contacts the stock material would signal that the press was approaching a theoretical pure carry through state. A theoretical pure carry through state would be achieved if slide bounce or swell, as the slide contacts the stock material was eliminated. Vibration introduced into the press structure from material fracture is lessened or potentially even eliminated as the press operating state tends toward a carry through condition. Similarly, the energy transfer requirements from the flywheel are lessened and may be potentially eliminated as press operating condition tends toward sufficient side kinetic energy which potentially achieves a theoretical pure carry through state.
What is needed in the art is a method and apparatus for monitoring the carry through condition of an operating press so that press operating conditions tending towards a theoretical pure carry through state can be determined and replicated and so that the requisite energy content of the slide required to achieve a carry through condition may be determined in order to reach a reduced level of vibration severity.
The present invention provides a method and apparatus for monitoring the carry through condition of a mechanical press. Specifically, the method and apparatus of the present invention utilizes measured quantities relating to the xe2x80x9cbouncexe2x80x9d, xe2x80x9creboundxe2x80x9d, or xe2x80x9cdwellxe2x80x9d experienced as the slide contacts the stock material to measure press operating condition relative to a carry through state. These measured quantities include the bounce point and the return point or the dwell length. The bounce point apex corresponds to the position of the slide that is furthest from the contact point, i.e., where the slide contacts the stock material, and is between the contact point and the top dead center point of the slide on the downstroke and is reached after the slide contacts the stock material. The xe2x80x9creturn pointxe2x80x9d corresponds to the point at which the slide returns to a position that is the same distance from top dead center on the slide downstroke as the contact point. The distance from the contact point to the bounce point and from the contact point to the return point as measured along the ordinate and the abscissa respectively are utilized as indicators of the carry through condition of the mechanical press. Bounce number is additionally utilized as an indicator of the carry through condition of a mechanical press. Bounce number is a quantity which indicates the cumulative number of bounces experienced as the slide contacts the stock material. Dwell length is the time the slide is held immobile or reversing due to failure of material to fracture or sheer on control or resistance to the slide.
Adjustments to press operational parameters may then be made in an effort to bring the operational state of the press being monitored closer to a theoretical pure xe2x80x9ccarry throughxe2x80x9d state. Press operational parameters which may be adjusted in an effort to achieve a carry through state for a mechanical press include increasing the energy of the slide. Increased slide energy will allow the slide to perform the desired forming activity while experiencing less significant xe2x80x9cbouncexe2x80x9d as the slide motion is resisted by the stock material. While slide energy can be increased both by increasing slide velocity and by increasing slide mass, or speed increasing slide mass is preferred since increasing slide velocity leads to a more severe vibrational state of the press. These adjustments ensure no snap through hesitation of the slide occurs and therefore no discontinuous spike of energy is needed from the flywheel to build up slide energy to achieve snap through.
The invention, in one form thereof, comprises a method of achieving a carry through state in a mechanical press. This method includes the steps of: determining the rebound height of the slide as it contacts the stock material and adjusting press operational parameters in an effort to minimize the rebound height of the slide as it contacts the stock material or minimize dwell lenght.
The invention, in another form thereof, comprises a method of achieving a carry through state in a mechanical press. This method includes the steps of: determining the rebound height of the slide as it contacts the stock material, determining the rebound count of the slide as it contacts the stock material, and adjusting press operational parameters in an effort to minimize both the rebound height and the rebound count of the slide as it contacts the stock material.
The invention, in another form thereof, comprises a method of achieving a carry through state in a mechanical press. This method includes the steps of: determining the rebound height of the slide as it contacts the stock material; determining the rebound count of the slide as it contacts the stock material; determining the rebound number of the slide as it contacts the stock material; and adjusting press operational parameters in an effort to minimize the rebound height, rebound count, and rebound number of the slide as it contacts the stock material.
In one form of the current invention, determining the rebound height of the slide as it contacts the stock material is achieved by: determining the contact point where the slide contacts the stock material, determining the bounce point which corresponds to the position of the slide that is furthest from the contact point and is between the contact point and the top dead center point of the slide on the slide downstroke and which is reached after the slide contacts the stock material, determining the distance along the slide path between the contact point and the bounce point, and establishing the distance along the slide path between the contact point and the bounce point as the rebound height. This method of determining the rebound height of the slide as it contacts the stock material may further include the steps of: providing a computational device, communicating the contact point to the computational device, communicating the bounce point to the computational device, and using the computational device to compute the distance along the slide path between the contact point and the bounce point.
In one form of the current invention, the step of determining the contact point where the slide contacts the stock material includes the steps of: creating an actual slide displacement curve, determining the first inflection point on the actual slide displacement curve, and establishing the first inflection point on the actual slide displacement curve as the contact point. The step of creating an actual slide displacement curve may further include the steps of: providing a non-contact displacement sensor, monitoring slide position continuously during press operation, and plotting slide displacement versus a count quantity. The step of plotting slide displacement versus a count quantity may comprise: plotting slide displacement versus time or crank angle.
In one form of the current invention, rebound count is determined by: determining the return point which corresponds to the slide returning to a position that is the same distance from top dead center on the slide downstroke as the contact point, determining the count quantity elapsing between the slide reaching the contact point and the slide reaching the return point, and establishing the count quantity elapsing between the slide reaching the contact point and the slide reaching the return point as the rebound count. Determining the rebound count of the slide may further include the steps of: communicating the return point to a computational device, communicating the contact point to a computational device, and using the computational device to determine the count quantity elapsing between the slide reaching the contact point and the slide reaching the return point.
In one form of the current invention, the step of adjusting press operational parameters in an effort to minimize either the rebound height or the rebound count of the slide as it contacts the stock material comprises the step of: increasing the energy of the slide. Increasing the energy of the slide may be achieved by adding mass to the slide.
In one form of the current invention, rebound number is determined by: determining all inflection points which occur on the actual slide displacement curve from the dynamic top dead center position of the slide to the dynamic bottom dead center position of the slide and calculating a quantity of rebound number utilizing the inflection points occurring on the actual slide displacement curve from the dynamic top dead center position of the slide to the dynamic bottom dead center position of the slide. The step of calculating a quantity of rebound number utilizing the inflection points occurring on the actual slide displacement curve may comprise the steps of: generating a cumulative number of inflection points occurring on the actual slide displacement curve from the dynamic top dead center position of the slide to the dynamic bottom dead center position of the slide and establishing the cumulative number of inflection points occurring on the actual slide displacement curve as the rebound number, or dividing the cumulative number of inflection points occurring on the actual slide displacement curve by two and establishing the cumulative number divided by two as the rebound number. Rebound number is indicative of the number of bounces occurring as the slide contacts the stock material.
The invention, in another form thereof, comprises a method of achieving a carry through state in a mechanical press. This method includes the steps of: determining the rebound count of the slide as it contacts the stock material and adjusting press operational parameters in an effort to minimize the rebound count or dwell length of the slide as it contacts the stock material.
The invention, in another form thereof, comprises a method of achieving a carry through state in a mechanical press. This method includes the steps of: determining the rebound number of the slide as it contacts the stock material and adjusting press operational parameters in an effort to minimize the rebound number of the slide as it contacts the stock material.
The invention, in another form thereof, comprises a method of decreasing the vibration severity level of a mechanical press. This method comprises the steps of: monitoring the carry through condition of the press and adjusting press operational parameters in response to the monitored carry through condition of the press to bring the operational state of the press being monitored closer to a carry through state. The step of monitoring the carry through condition of the press may comprise the step of: determining the rebound height and/or rebound count and/or rebound number of the slide as it contacts the stock material.
In one form of the current invention, the step of adjusting press operational parameters in response to the monitored carry through condition of the press to bring the operational state of the press being monitored closer to a carry through state comprises the step of: increasing the kinetic energy of the slide. Increasing the kinetic energy of the slide may be accomplished by adding mass to the slide.
The invention, in another form thereof, comprises an apparatus useful to achieve a carry through state in a mechanical press having a reciprocating slide. The apparatus of this form of the current invention includes a computational device, a displacement sensor, and a display device. The displacement sensor is operatively connected to the press so that the displacement sensor may sense the location of the press slide during press operation. The displacement sensor is communicatively connected to the computational device and the computational device is operative to continually create an actual slide displacement curve for each pressing cycle of the press being monitored. The computational device is further operative to obtain values of rebound height and rebound count from the thusly generated slide displacement curves. The display device is communicatively connected to the computational device and is operative to display the computed values of rebound height and rebound count. The computational device may be, for example, a microprocessor. The displacement sensor may be a non-contact displacement sensor, for example, a hall effect sensor. The slide includes a plurality of areas operable for adding mass to the slide and therefore, increasing the kinetic energy of the slide in response to the displayed values of rebound height and rebound count.
An advantage of the present invention is the ability to monitor press performance characteristics which are indicative of the carry through condition of the press being monitored.
Another advantage of the present invention is the ability to utilize indicators of press carry through condition so that press operational parameters may be adjusted in an effort to create a press operational state closer to carry through and to achieve the reduction in press vibration severity resulting therefrom.
A further advantage of the present invention is the ability to recognize the energy state of the slide required to achieve a carry through condition in a mechanical press and to decrease the size of or eliminate entirely the flywheel based upon the energy state of the slide.